U.S. patent number 5,858,174 [Application Number 08/676,763] was granted by the patent office on 1999-01-12 for process for the production of paper.
This patent grant is currently assigned to Eka Chemicals AB. Invention is credited to Joakim Carlen, Carlos Cordoba, Hans Johansson, Michael Persson.
United States Patent |
5,858,174 |
Persson , et al. |
January 12, 1999 |
**Please see images for:
( Certificate of Correction ) ** |
Process for the production of paper
Abstract
The invention relates to a process for the production of paper
from a suspension of cellulose containing fibers, and optional
fillers, comprising adding to the suspension a low molecular weight
cationic organic polymer, a high molecular weight cationic or
amphoteric polymer and anionic inorganic particles, forming and
draining the suspension on a wire, wherein the low molecular weight
polymer has a molecular weight below 700,000 and the high molecular
weight polymer has a molecular weight above 1,000,000, said
polymers being simultaneously added to the suspension. The
invention further relates to a polymer mixture in the form of an
aqueous dispersion comprising at least one high molecular weight
cationic or amphoteric acrylamide-based polymer having a molecular
weight above 1,000,000, at least one low molecular weight cationic
organic polymer having a molecular weight below 700,000 and at
least one water-soluble inorganic salt, the weight ratio of said
high molecular weight polymer to said low molecular weight polymer
being within the range of from 9:1 to 1:2.
Inventors: |
Persson; Michael (Goteborg,
SE), Carlen; Joakim (Varberg, SE),
Johansson; Hans (Kungalv, SE), Cordoba; Carlos
(Barcelona, ES) |
Assignee: |
Eka Chemicals AB (Bohus,
SE)
|
Family
ID: |
20398921 |
Appl.
No.: |
08/676,763 |
Filed: |
July 8, 1996 |
Foreign Application Priority Data
Current U.S.
Class: |
162/164.1;
162/181.8; 162/181.4; 162/181.1; 162/175; 162/168.3; 162/168.2;
162/168.1; 162/164.6; 162/164.3; 162/181.5; 162/181.6; 162/183 |
Current CPC
Class: |
D21H
17/375 (20130101); D21H 17/55 (20130101); C08L
33/26 (20130101); D21H 17/56 (20130101); D21H
17/29 (20130101); D21H 17/68 (20130101); D21H
23/04 (20130101); D21H 17/455 (20130101); C08L
33/26 (20130101); C08L 2666/04 (20130101); C08L
3/04 (20130101); C08L 2205/02 (20130101); C08L
79/02 (20130101); C08L 2201/50 (20130101) |
Current International
Class: |
C08L
33/26 (20060101); D21H 17/56 (20060101); D21H
23/00 (20060101); D21H 17/00 (20060101); D21H
17/55 (20060101); D21H 17/37 (20060101); D21H
17/29 (20060101); C08L 33/00 (20060101); D21H
17/45 (20060101); D21H 23/04 (20060101); D21H
17/68 (20060101); C08L 79/00 (20060101); C08L
79/02 (20060101); C08L 3/04 (20060101); C08L
3/00 (20060101); D21H 021/10 () |
Field of
Search: |
;162/164.1,164.3,164.6,168.1,168.2,168.3,175,183,181.1,181.6,181.8,181.4,181.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0 183 466 |
|
Jun 1986 |
|
EP |
|
0 223 223 |
|
May 1987 |
|
EP |
|
0 308 752 |
|
Mar 1989 |
|
EP |
|
0 335 575 |
|
Oct 1989 |
|
EP |
|
0 525 751 |
|
Feb 1993 |
|
EP |
|
0 656 872 |
|
Jun 1995 |
|
EP |
|
WO 94/05595 |
|
Mar 1994 |
|
WO |
|
WO 95/23021 |
|
Aug 1995 |
|
WO |
|
Other References
Abstract, NZ 140,574, Process For Dry-Strengthening Paper, Patent
Office Journal, No. 1073, Oct. 1968..
|
Primary Examiner: Chin; Peter
Attorney, Agent or Firm: Mancini; Ralph J.
Claims
We claim:
1. A process for the production of paper which comprises providing
a suspension of cellulose containing fibers, and optional fillers;
adding to said suspension i) at least one low molecular weight
cationic organic polymer having a molecular weight below 700,000
selected from the group consisting of modified starches,
polyamines, polyethylene imine polyamideamine/-epichlorohydrin,
dialkylamine/epichlorohydrin, homo-and copolymers based on monomers
selected from diallyldimethyl ammonium chloride vinyl amines (meth
acrylamides, and (meth) acrylates; ii) at least one high molecular
weight cationic or amphoteric polymer drainage and/or retention aid
having a molecular weight above 1,000,000 selected from the group
consisting of cationic and amphoteric starches, guar gums,
acrylamide-based polymers, N-vinylamide-based polymers,
diallyldi-methyl ammonium chloride-based polymers cationic
polyethylene imines, polyamines and polyamedeamines; said low
molecular weight and high molecular weight polymers being added in
an amount of at least 0.01 kg/ton to 30 kg/ton, calculated as dry
polymers on dry fibers and optional fillers, the weight ratio of
said high molecular weight polymer to said low molecular weight
polymer being within the range of from 30:1 to 1:20, wherein said
low molecular weight polymer and said high molecular weight polymer
are simultaneously added to the suspension at essentially the same
position in the stock preparation or paper machine; and (iii)
anionic inorganic particles selected from the group consisting of
silica based particles, clays of the smectite type, titanyl
sulphate sols, and mixtures thereof, said particles being added in
an amount of at least 0.01 kg/ton, calculated as dry particles on
dry fibers and optional fillers; and forming and draining the
obtained suspension on a wire to form paper.
2. The process of claim 1, wherein the low molecular weight polymer
and the high molecular weight polymer are added to the suspension
in the form of a mixture.
3. The process of claim 1, wherein the low molecular weight polymer
and the high molecular weight polymer are simultaneously but
separately added to the suspension.
4. The process of claim 1, wherein the high molecular weight
polymer is cationic starch, cationic guar gum or cationic
acrylamide-based polymer.
5. The process of claim 1, wherein the low molecular weight
cationic polymer is modified starch, polyamine, polyethylene imine,
polyamideamine/epichlorohydrin, dimethylamine/epichlorohydrin or a
homo- or copolymer based on monomers selected from diallyldimethyl
ammonium chloride, vinylamines, (meth)acrylamides, or
(meth)acrylates, or mixtures thereof.
6. The process of claim 5, wherein the low molecular weight
cationic polymer is polyamine, polyethylene imine,
polyamideamine/epichlorohydrin or
dimethylamine/epichlorohydrin.
7. The process of claim 1, wherein the low molecular weight
cationic polymer has a higher cationic charge density than the high
molecular weight polymer.
8. The process of claim 1, wherein the low molecular weight polymer
has a molecular weight within the range of from about 5,000 to
about 500,000; and the high molecular weight polymer has a
molecular weight above about 2,000,000.
9. The process of claim 1, wherein the weight ratio of high
molecular weight polymer to low molecular weight polymer is within
the range of from 9:1 to 1:3.
10. The process of claim 1, wherein the polymers are added in a
total amount of from 0.01 to 30 kg/ton, calculated as dry polymers
on dry fibers and optional fillers.
11. The process of claim 1, wherein the anionic inorganic particles
are silica based.
12. The process of claim 11, wherein the silica based particles
have a particle size within the range of from about 1 to about 10
nm.
13. The process of claim 11, wherein the silica based particles are
colloidal silica, colloidal aluminum modified silica, aluminum
silicate or polysilicic acid.
14. The process of claim 1, wherein the anionic inorganic particles
are bentonite.
15. The process of claim 1, wherein the anionic inorganic particles
are added in an amount of from 0.05 to 10 kg/ton, calculated as dry
particles on dry fibers and optional fillers.
16. A process for the production of paper which comprises providing
a suspension containing cellulosic fibers, and optional fillers;
adding to said suspension
(i) a low molecular weight cationic organic polymer having a
molecular weight within the range of from 2,000 to 700,000 selected
from the group consisting of polyamines, polyethylene imines,
polyamideamine/epichlorohydrin, dialkylamine/epichlorohydrin,
homo-and copolymers based on monomers selected from
diallyl-dimethyl ammonium chloride, vinylamines, (meth)acrylamides,
and (meth)acrylates, and mixtures thereof;
(ii) a high molecular weight polymer having a molecular weight
above 1,000,000 selected from the group consisting of cationic and
amphoteric starches, cationic and amphoteric guar gums, cationic or
amphoteric acrylamide-based polymers, and mixtures thereof; said
low molecular weight and high molecular weight polymers being added
in the form of a mixture or added separately but simultaneously at
essentially the same position in the stock preparation or paper
machine in an amount of from 0.01 to 30 kg/ton, calculated as dry
polymers on dry fibers and optional fillers, the weight ratio of
said high molecular weight polymer to said low molecular weight
polymer being within the range of from 20:1 to 1:20, and
(iii) anionic inorganic particles selected from the group
consisting of colloidal silica, colloidal aluminum-modified silica,
aluminum silicate, polysilicic acids, and mixtures thereof, the
particles being added in an amount within the range of from 0.05 to
10 kg/ton, calculated as dry particles on dry fibers and optional
fillers; forming and draining the obtained suspension on a wire to
form paper.
17. The process of claim 16, wherein the high molecular weight
polymer is a cationic acrylamide-based polymer.
18. The process of claim 16, wherein the high molecular weight
polymer is cationic starch.
19. The process of claim 16, wherein the low molecular weight
polymer has a higher cationicity and/or higher cationic charge
density than the high molecular weight polymer.
20. The process of claim 16, wherein the polymers are added in the
form of a mixture.
Description
The present application claims priority of Swedish application no.
9502522-7, filed Jul. 7, 1995 and benefit of U.S. Provisional
patent application Ser. No. 60/001,242, filed Jul. 19, 1995.
The present invention relates to a process for the production of
paper and, more particularly, to a process in which a low molecular
weight cationic polymer, a high molecular weight charged polymer
and anionic inorganic particles are added to a papermaking stock.
The process provides improved drainage and retention.
BACKGROUND
It is known in the art to use systems of drainage and retention
aids comprising high molecular weight (hereafter HMW) charged
polymers and anionic inorganic particles, e.g. bentonite and silica
based particles. These additives are introduced into the stock in
order to facilitate drainage and increase adsorption of fine
particles onto the cellulose fibers so that they are retained with
the fibers. However, the efficiency of drainage and retention aids
usually is deteriorated in stocks which have a high cationic demand
due to the presence of interfering anionic substances. In the art,
such substances are commonly referred to as anionic trash. The
level of anionic trash usually is high in stocks based on recycled
fibers and mechanically derived pulps. To counter the deteriorated
performance of additives observed in such stocks, it is known to
use low molecular weight (hereafter LMW) cationic polymers as
anionic trash catchers which are initially added to the stock in
order to neutralize the anionic trash and reduce the cationic
demand, thereby enhancing the efficiency of drainage and retention
aids subsequently added.
European Patent Application No. 0335575 discloses a process for the
production of paper which comprises a preliminary polymer inclusion
stage in which a LMW cationic polymer is added to a cellulosic
suspension followed by addition of a main polymer selected from
cationic starch or HMW cationic polymer and then an inorganic
material selected from bentonite or colloidal silica.
European Patent Application No. 0308752 relates to a method for
making paper which comprises the steps of adding to paper furnish a
LMW cationic organic polymer and then colloidal silica and a HMW
charged acrylamide copolymer having a molecular weight of at least
500,000.
THE INVENTION
According to the present invention it has been found that very good
drainage and/or retention can be obtained with additives comprising
LMW cationic polymer, HMW cationic and/or amphoteric polymer and
anionic inorganic particles when the LMW cationic polymer and HMW
cationic and/or amphoteric polymer are simultaneously added to the
stock, in particular when using the LMW polymer and HMW polymer in
the form of a mixture. This discovery is contrary to prior art
techniques which emphasize the initial addition of LMW cationic
polymers for obtaining adequate performance with subsequently added
drainage and retention aids comprising HMW charged polymers and
anionic inorganic particles. More specifically, the present
invention relates to a process for the production of paper from a
suspension of cellulose containing fibers, and optional fillers,
which comprises adding to the suspension a low molecular weight
cationic organic polymer, a high molecular weight cationic and/or
amphoteric polymer and anionic inorganic particles, forming and
draining the suspension on a wire, wherein the low molecular weight
polymer has a molecular weight below 700,000; the high molecular
weight polymer has a molecular weight above 1,000,000; and said
polymers are simultaneously added to the suspension. The invention
thus relates to a process as further defined in the claims.
The process according to the present invention results in improved
drainage and/or retention compared to processes in which HMW
cationic or amphoteric polymers are used as a sole polymer additive
in conjunction with anionic inorganic particles. Furthermore, the
present process results in improved drainage and/or retention
compared to processes comprising pre-dosing LMW cationic polymer
prior to adding HMW cationic and/or amphoteric polymers and anionic
inorganic particles. Hereby the present invention makes it possible
to increase the speed of the paper machine and to use lower dosages
of additives to give the same drainage and/or retention effect,
which lead to an improved papermaking process and economic
benefits.
The polymers simultaneously added to the stock according to the
invention comprise at least one high molecular weight charged
polymer that functions as a drainage and/or retention aid. The HMW
polymer can be selected from cationic polymers, amphoteric polymers
or mixtures thereof. The use of such polymers as drainage and/or
retention aids is known in the art. Preferred HMW polymers are
water-soluble. Suitably at least one HMW cationic organic polymer
is used. Generally, the cationicity of the HMW polymers can be
within the range of from 1 to 100 mole %, suitably from 1 to 80
mole % and preferably from 1 to 60 mole %. The term "cationicity",
as used herein, refers to the amount of cationic mer units present
in the polymer. The charge density of the HMW polymer can be from
200 to 7,000 .mu.eq/g of dry polymer. The HMW polymer can be
derived from natural or synthetic sources, and it can be linear or
branched. Examples of suitable polymers include cationic and
amphoteric starches, guar gums, acrylamide-based and
N-vinylamide-based polymers, polymers based on
diallyldimethylammonium chloride and cationic polyethylene imines,
polyamines and polyamideamines. Cationic starches, guar gums and
acrylamide-based polymers are preferred HMW polymers. The molecular
weight of the HMW polymer suitably is above 1,000,000 and
preferably above 2,000,000. The upper limit is not critical; it can
be about 50,000,000, usually 30,000,000 and suitably 25,000,000.
However, the molecular weight of polymers derived from natural
sources may be higher.
The polymers simultaneously added to the stock according to the
invention further comprises at least one low molecular weight
cationic organic polymer. Preferred polymers include water-soluble,
highly charged LMW polymers which can have a cationicity of from 10
to 100 mole %, suitably from 20 to 100 mole % and preferably from
50 to 100 mole %. The charge density of the LMW polymer can be
above 1,000 .mu.eq/g, suitably above 2,000 .mu.eq/g and preferably
within the range of from 3,000 to 15,000 .mu.eq/g of dry polymer.
It is preferred that the LMW polymer has a higher cationicity
and/or higher cationic charge density than the HMW polymer.
Examples of suitable LMW cationic polymers include modified
starches, e.g. degraded starch, polyamines, polyethylene imine,
polyamideamine/-epichlorohydrin, dialkylamine/epichlorohydrin,
homo- and copolymers based on monomers selected from
diallyldimethylammonium chloride, vinyl amines, (meth)acrylamides
and (meth)acrylates. Preferred LMW cationic polymers include
polyamines, polyethylene imines, epichlorohydrin-based polymers and
diallyldimethylammonium chloride-based polymers. The cationic
monomers can be acid addition salts and/or quaternary ammonium
salts. Examples of suitable (meth)acrylamides and (meth)acrylates
include dialkylaminoalkyl (meth)acrylamides and dialkylaminoalkyl
(meth)acrylates, preferably their quaternary ammonium salts. The
moleclar weight of the LMW cationic polymer may depend on the type
of polymer and its charge density. Suitably the molecular weight is
below 700,000 and preferably below 500,000. The lower limit is
usually 2,000 and preferably about 5,000.
The weight ratio of HMW polymer to LMW polymer added to the stock
according to the invention can be varied over a broad range and it
can be within the range from 30:1 to 1:20, usually from 20:1 to
1:20, suitably from 9:1 to 1:3, preferably from 7:1 to 1:2 and most
preferably from 5:1 to 1:1.
The simultaneous addition to the stock of the HMW and LMW polymers
according to the invention can be conducted at any position in the
paper machine or stock preparation department. Hereby is meant that
the polymers are added to the stock with substantially no time
difference and essentially at the same position in the stock
preparation department or paper machine prior to draining the stock
on the wire. This means that the polymers can be added in the form
of a mixture as well as separately, e.g. by adding one polymer
during the addition of the other.
According to a preferred embodiment of the invention, the LMW
cationic polymer in admixture with the HMW cationic and/or
amphoteric polymer are added to the stock. The use of a polymer
mixture and anionic inorganic particles according to the invention
provides considerable improvements over prior art processes, in
particular improved retention performance in stocks having a high
cationic demand. The addition of a polymer mixture containing both
LMW polymer and HMW polymer is further advantageous from an
operational viewpoint since the number of polymer additions
required can be reduced. Hereby it is possible to dispense with
storage tanks, dosing equipment, control devices, etc., otherwise
needed for polymer dosage, leading to a simplified papermaking
process.
The polymer mixture of this embodiment can be prepared at any time
prior to incorporating it into the stock, for example by mixing the
polymers which may be in any state of aggregation, e.g. solids,
solutions, emulsions, dispersions and mixtures thereof. When being
added to the stock, the polymer mixture suitably is in a liquid
form, e.g. in the form of an aqueous solution or dispersion.
In a preferred embodiment, use is made of a freshly prepared
mixture of HMW polymer and LMW polymer, as defined above. Such a
pre-mix can be formed by bringing an aqueous stream of HMW polymer
into contact with an aqueous stream of LMW polymer and then
introducing the resulting stream into the suspension. If desired,
the streams can be mixed by means of any mixing device having at
least two inlets into which separate streams of the polymers to be
mixed are supplied and having at least one outlet through which the
resulting mixture is passed and subsequently introduced into the
stock.
The present invention further relates to a mixture of water-soluble
polymers in the form of an aqueous dispersion containing at least
one HMW polymer, at least one LMW cationic organic polymer and at
least one water soluble inorganic salt, as further defined in the
claims. The invention also relates to a method for its preparation.
The polymer mixture provides improved drainage and/or retention
when used in combination with anionic inorganic particles. In the
polymer mixture according to the invention, the HMW polymer
suitably is a cationic and/or amphoteric acrylamide-based polymer,
preferably a cationic acrylamide-based polymer. The HMW polymer can
have a cationicity ranging from 1 to 100 mole %, suitably from 1 to
80 mole % and preferably from 1 to 60 mole %, and it can have a
charge density within the range of from 200 to 7,000 .mu.eq/g of
dry polymer. The molecular weight of the HMW polymer suitably is
above 1,000,000 and preferably above 2,000,000. The upper limit is
not critical; it can be about 50,000,000, usually 30,000,000 and
suitably 25,000,000. The LMW cationic polymer preferably is a homo-
or copolymer based on monomers selected from
diallyldimethylammonium chloride, vinylamines, (meth)acrylamides,
e.g. dialkylaminoalkyl (meth)acrylamides, (meth)acrylates, e.g.
dialkylaminoalkyl (meth)acrylates, or mixtures thereof. The
cationic monomers can be acid addition salts and/or quaternary
ammonium salts, preferably quaternary ammonium salts. The LMW
cationic polymer can have a cationicity within the range of from 10
to 100 mole %, suitably from 20 to 100 mole % and preferably from
50 to 100 mole %, and it can have a charge density above 1,000
.mu.eq/g, suitably above 2,000 .mu.eq/g and preferably within the
range of from 3,000 to 15,000 .mu.eq/g of dry polymer. It is
preferred that the LMW polymer has a higher cationicity and/or
higher cationic charge density than the HMW polymer. The weight
ratio of HMW polymer to LMW polymer can be within the range of from
9:1, suitably from 7:1 and preferably from 5:1, to 1:2, suitably to
1:1 and preferably to 2:1. The aqueous dispersion of polymers can
have a high dry polymer content, e.g. ranging from 5 to 75% by
weight and suitably from 10 to 60% by weight.
In the polymer mixture according to the invention, it is preferred
that the inorganic salt is an inorganic salt producing an aqueous
phase in which the HMW polymer is insoluble. Examples of suitably
salts include sodium sulfate, ammonium sulfate, magnesium sulfate,
aluminum sulfate, sodium chloride, sodium dihydrogenphosphate,
diammonium hydrogenphosphate and dipotassium hydrogenphosphate.
Generally, polyvalent anion salts are preferred, e.g. the sulfates.
The amount of water-soluble salt present in the polymer dispersions
can be at least 2% by weight, based on the dispersion, and suitably
the amount is within the range of from about 5% up to the limit of
solubility of the salt, e.g. up to 50%.
The subject polymer mixture can be obtained by polymerization of
water-soluble monomers intended for formation of the HMW polymer in
an aqueous phase containing the LMW cationic polymer and the
inorganic salt. Examples of suitable monomers include
(meth)acrylamide, (meth)acrylamide-based monomers, e.g.
dialkylaminoalkyl (meth)acrylamides, acid addition salts and
quaternary ammonium salts thereof, (meth)acrylate-based monomers,
e.g. dialkylaminoalkyl (meth)acrylates, acid addition salts and
quaternary ammonium salts thereof, diallyldialkylammonium halides,
e.g. diallyldimethylammonium chloride, and the like. The HMW
polymer formed is precipitated in the aqueous phase due to the
presence of the inorganic salt and the fine particles of HMW
polymer so obtained are dispersed and stabilized in the aqueous
phase by means of the LMW polymer. Generally, the polymerization of
monomers in the presence of salt and polymeric dispersing agents is
known in the art, for example from EP 0183466 and EP 0525751, and
the present polymer mixture can be prepared according to the
methods disclosed therein except that other polymers and/or weight
ratios are used to produce the polymer mixture of the present
invention.
The amount of polymers added to the stock according to the process
of the present invention can be varied over a broad range depending
on, among other things, the type of polymers used and if the
polymers are utilized for further purposes. In addition to
providing drainage and/or retention, the polymers may impart
wet-strength and dry-strength to the cellulosic web or sheet
produced. Examples of wet-strength improving polymer combinations
include HMW cationic starch and cationic acrylamide-based polymer
in combination with polyamideamine/epichlorohydrin. Usually, the
total amount of polymers added is within the range of from 0.01 to
30 kg/ton, calculated as dry polymers on dry fibers and optional
fillers. When using synthetic HMW polymers, e.g. cationic
polyacrylamides, the total amount of polymers usually is at least
0.01 kg/ton, suitably from 0.02 to 15 kg/ton and preferably from
0.05 to 8 kg/ton. When using HMW polymers derived from natural
sources such as those based on carbohydrates, e.g. cationic starch
and cationic guar gum, the total amount of polymers usually is at
least 0.05 kg/ton, calculated as dry polymers on dry fibers and
optional fillers, suitably from 0.1 to 30 kg/ton and preferably
from 1 to 20 kg/ton.
Anionic inorganic particles that can be used according to the
invention include silica based particles, clays of the smectite
type and titanyl sulphate sols. It is preferred that the particles
are colloidal, i.e. in the colloidal range of particle size. It is
preferred to use silica based particles, i.e. particles based on
SiO.sub.2, including colloidal silica, colloidal aluminum-modified
silica or aluminum silicate, different types of polysilicic acid
and mixtures thereof, either alone or in combination with other
types of anionic inorganic particles. Suitable silica based
particles include those disclosed in U.S. Pat. Nos. 4,388,150,
4,954,220, 4,961,825, 4,980,025, 5,127,994, 5,176,891, 5,368,833,
5,447,604, EP 0656872, and WO 95/23021, which are all hereby
incorporated herein by reference.
The silica based particles suitably have a particle size below
about 50 nm, preferably below about 20 nm and more preferably in
the range of from about 1 to about 10 nm. The silica based
particles suitably have a specific surface area above 50 m.sup.2
/g, preferably above 100 m.sup.2 /g, and suitably up to about 1700
m.sup.2 /g. The specific surface area can be measured by means of
titration with NaOH according to the method described by Sears in
Analytical Chemistry 28(1956):12, 1981-1983.
According to a preferred embodiment of the invention, the silica
based particles have a specific surface area within the range of
from 50 to 1000 m.sup.2 /g and suitablty from 100 to 950 m.sup.2
/g. In a particularly preferred embodiment, use is made of a silica
sol having an S-value within the range of from 8 to 45%, preferably
from 10 to 30%, containing silica particles having a specific
surface area within the range of from 750 to 1000 m.sup.2 /g,
preferably from 800 to 950 m.sup.2 /g, which are surface-modified
with aluminum to a degree of from 2 to 25% substitution of silicon
atoms, as disclosed in U.S. Pat. No. 5,368,833. The S-value can be
measured and calculated as described by Iler & Dalton in J.
Phys. Chem. 60(1956), 955-957. The S-value indicates the degree of
aggregate or microgel formation and a lower S-value is indicative
of a higher degree of aggregation.
According to another preferred embodiment of the invention, use is
made of a polysilicic acid having a high specific surface area,
suitably above about 1000 m.sup.2 /g. In the art, polysilicic acid
is also referred to as polymeric silicic acid, polysilicic acid
microgel and polysilicate microgel, which are all encompassed by
the term polysilicic acid. Suitably, the polysilicic acid has a
specific surface area within the range of from 1000 to 1700 m.sup.2
/g, preferably from 1050 to 1600 m.sup.2 /g. Polysilicic acids that
can be used according to the present invention include those
disclosed in U.S. Pat. Nos. 4,388,150, 4,954,220, 5,127,994 and
5,279,807.
According to another preferred embodiment of the invention, use is
made of colloidal aluminum-modified silica or aluminum silicate
having a high specific surface area, suitably above about 1000
m.sup.2 /g. In the art, compounds of this type are also referred to
as polyaluminosilicates and polyaluminosilicate microgels, which
are both encompassed by the terms colloidal aluminum-modified
silica and aluminum silicate used herein. Suitably, the specific
surface area is within the range of from 1000 to 1700 m.sup.2 /g,
preferably from 1050 to 1600 m.sup.2 /g. Examples of suitable high
surface area silica based particles of this type include those
disclosed in U.S. Pat. Nos. 4,961,825, 4,980,025, 4,927,498,
5,176,891 and 5,470,435.
Clays of the smectite type that can be used in the present process
are known in the art and include naturally occurring, synthetic and
chemically treated materials. Examples of suitable smectite clays
include montmorillonite/-bentonite, hectorite, beidelite,
nontronite and saponite, preferably bentonite and especially such
which after swelling preferably has a surface area of from 400 to
800 m.sup.2 /g. Suitable bentonites and hectorites are disclosed in
EP 0235893 and EP 0446205, respectively, which are both
incorporated herein by reference. Suitable mixtures of silica based
particles and smectite clays, preferably natural sodium bentonite,
are disclosed in WO 94/05595 which is likewise incorporated herein
by reference, wherein the weight ratio of silica based particles to
clay particles can be in the range of from 20:1 to 1:10, preferably
from 6:1 to 1:3. Useful titanyl sulphate sols are for example
disclosed in EP 0148647.
The amount of anionic inorganic particles added to the suspension
may vary within wide limits depending on, among other things, the
type of particles used. The amount usually is at least 0.01 kg/ton
and often at least 0.05 kg/ton, calculated as dry particles on dry
fibers and optional fillers. The upper limit can be 10 kg/ton and
suitably is 5 kg/ton. When using silica based particles, the amount
suitably is within the range of from 0.05 to 5 kg/ton, calculated
as SiO.sub.2 on dry stock system, and preferably from 0.1 to 2
kg/ton.
In the present process it is preferred to add the polymers to the
stock before the anionic inorganic particles, even if the opposite
order of addition may be used. It is further preferred to add the
first component, e.g. the polymers, before a shear stage which can
be selected for example from pumping, mixing, cleaning, etc., and
to add the second component, e.g. the anionic inorganic particles,
after that shear stage. The present process further encompasses
split additions, e.g. at least two positions for simultaneously
adding the polymers, either separately or in admixture, and/or at
least two positions for adding anionic inorganic particles,
preferably with a shear stage between each addition. The high
dewatering and retention effects observed with the additives of the
invention can be obtained over a broad stock pH range. The pH can
be in the range from about 3 to about 10, suitably above 3.5 and
preferably within the range of from 4 to 9.
Additives which are conventional in papermaking such as, for
example, stock sizes based on rosin, ketene dimers or alkenyl
succinic anhydrides, dry strength agents, wet strength agents,
aluminum compounds, etc., can of course be co-used in the process
of the invention. The improved performance observed in the process
of the present invention means that further benefits can be
obtained, such as for example improved retention of such additives
which can lead to improved sizing and strength of the paper.
Aluminum compounds can be used to further improve drainage and/or
retention in the present process. Examples of suitable aluminum
compounds that can be used include alum, aluminates, aluminum
chloride, aluminum nitrate and polyaluminum compounds, such as
polyaluminum chlorides, polyaluminum sulphates, polyaluminum
compounds containing both chloride and sulphate ions and
polyaluminum silicate-sulphates. The suspension or stock can also
contain mineral fillers of conventional types such as, for example,
kaolin, china clay, titanium dioxide, gypsum, talc and natural and
synthetic calcium carbonates such as chalk, grinded marble and
precipitated calcium carbonate.
The process according to the invention can be used for producing
cellulose fiber containing products in sheet or web form such as
for example pulp sheets and paper. It is preferred that the present
process is used for the production of paper. The term "paper", as
used herein, of course include not only paper and the production
thereof, but also other sheet or web-like products, such as for
example board and paperboard, and the production thereof.
The process according to the invention can be used in the
production of sheet or web-like products from different types of
aqueous suspensions containing cellulosic fibers, or stocks, and
the suspensions suitably contain at least 25% by weight and
preferably at least 50% by weight of such fibers, based on dry
substance. The suspensions can be based on fibers from chemical
pulp such as sulphate and sulphite pulp, mechanical pulp such as
thermomechanical pulp, chemo-thermomechanical pulp, refiner pulp
and groundwood pulp, from both hardwood and softwood, and can also
be based on recycled fibers from de-inked pulps, and mixtures
thereof. It is preferred that at least l0o by weight and preferably
at least 20% by weight of the pulp is derived from recycled fiber,
de-inked pulp, coated broke or mechanical pulp or any mixture
thereof. Such stocks, normally, have a high cationic demand and
contains high levels of anionic trash which may be pulping
residues, bleaching residues, de-inking residues, binders, inks,
fillers, fines, sizes, dispersing agents and deposit control
chemicals.
The invention is further illustrated in the following Examples
which, however, are not intended to limit same. Parts and % relate
to parts by weight and % by weight, respectively, unless otherwise
stated.
EXAMPLE 1
In the following tests, drainage performance was evaluated by means
of a Dynamic Drainage Analyser (DDA), available from Akribi,
Sweden, which measures the time for draining a set volume of stock
through a wire when removing a plug and applying a vacuum to that
side of the wire opposite to the side on which the stock is
present.
The furnish contained 54% of pulp based on a 60:40 mixture of
bleached birch:pine sulphate refined to 200.degree. CSF, 23% of
grinded marble and 23% of coated broke (magazine paper) having an
ash content of 30%. Stock volume was 800 ml, consistency 0.3% and
pH about 7. The stock was stirred in a baffled jar at a speed of
1500 rpm throughout the test and chemical additions to the stock
were conducted as follows: i) adding either HMW polymer used for
comparison purposes or polymers according to the invention followed
by stirring for 30 seconds, ii) adding anionic inorganic particles
followed by stirring for 15 seconds, iii) draining the stock while
automatically recording the drainage time.
A polymer mixture, herein designated M1, in the form of an aqueous
dispersion of a HMW cationic polyacrylamide and a LMW cationic
polyacrylate was used in the process of the invention. The polymer
mixture was prepared by polymerization of acrylamide (90 mole %)
and methacryloyloxyethyldimethylbenzylammonium chloride (10 mole %)
to an average molecular weight of about 8 million in the presence
of a homopolymer of acryloyloxyethyltrimethylammonium chloride
having a molecular weight of about 10,000; deionized water;
ammonium sulphate and a polymerization initiator. The resulting
polymer mixture had a weight ratio HMW polymer to LMW polymer of
2.7:1, and a dry polymer content of about 18.5%. The polymer
mixture was diluted to a dry polymer content of 0.1% prior to
use.
Polymers used for comparison purposes were: P1) a HMW cationic
polyacrylamide having a molecular weight of about 8 million; and
P2) a HMW cationic polyacrylamide having a molecular weight of
about 16 million. The polymers P1 and P2 were dissolved in water
and used as 0.1% aqueous solutions.
The anionic inorganic material used was a silica based sol of the
type disclosed in U.S. Pat. No. 5,368,833. The sol had an S-value
of about 25% and contained silica particles with a specific surface
area of about 900 m.sup.2 /g which were surface-modified with
aluminum to a degree of 5%. This sol is designated Sol 1. Sol 1 was
added in an amount of 0.8 kg/ton, calculated as dry particles on
dry stock system.
Table 1 shows the drainage time at varying dosages of P1, P2 and
M1, calculated as dry polymer on dry stock system.
TABLE 1 ______________________________________ Polymer Drainage
time [seconds] at polymer dosage of used 0.5 kg/ton 0.8 kg/ton 1.2
kg/ton 2.0 kg/ton ______________________________________ P1 15.7
15.4 11.4 6.3 P2 15.7 14.0 11.8 6.6 M1 14.9 13.0 7.5 4.8
______________________________________
As can be seen from Table 1, the process using the mixture of LMW
and HMW cationic polymers according to the invention resulted in
improved drainage.
EXAMPLE 2
In this test series, retention was evaluated by means of the DDA
used in Example 1 in combination with a nephelometer. First pass
retention was evaluated by measuring the turbidity of the filtrate,
the white water, obtained by draining the stock. The polymers and
anionic inorganic particles according to Example 1 were similarly
used in this test series.
Table 2 shows the retention effect measured as turbidity of white
water obtained at varying dosages of P1, P2 and M1, calculated as
dry polymer on dry stock system.
TABLE 2 ______________________________________ Polymer Turbidity
[NTU] at polymer dosage of used 0.5 kg/ton 0.8 kg/ton 1.2 kg/ton
2.0 kg/ton ______________________________________ P1 236 149 87 42
P2 246 165 100 40 M1 161 90 53 29
______________________________________
As can be seen from Table 2, the process according to the invention
using a mixture of HMW and LMW cationic polymers resulted in
markedly improved first pass retention.
EXAMPLE 3
Retention was evaluated as in Example 2, except that different
polymers were used. The order of addition according to Example 1
was applied, unless otherwise indicated.
A polymer mixture designated M2 was prepared by dissolving the HMW
cationic polyacrylamide P2 according to Example 1 in an aqueous
solution of a LMW cationic polyamine having a molecular weight of
50,000, which is designated P3. M2 had a weight ratio P2 to P3 of
2.7:1.
Another embodiment of the invention was tested in which use was
made of a freshly prepared mixture of P2 and P3. An aqueous
solution of P2 was brought into contact with an aqueous solution of
P3 by means of a mixing device, where the separate solutions were
intimately mixed for about 2-3 seconds prior to introducing the
resulting solution into the stock. The polymers were added in a
weight ratio P2 to P3 of 2.7:1. This mixture is designated M3.
A further embodiment of the invention, designated S1, was tested in
which P2 and P3 were separately but simultaneously added to the
stock in a weight ratio P2 to P3 of 2.7:1.
P2 and P3 were also used for comparison purposes, where P3 was
added to the stock followed by stirring for 120 seconds before
adding P2. The polymers were used in an amount corresponding to a
weight ratio P2 to P3 of 2.7:1. In Table 3, this test is designated
P3+P2. In one test, P2 was also used as a single cationic polymer
additive.
Table 3 shows the retention effect observed when adding 1.2 kg of
total polymer and 0.8 kg of silica based particles per ton of dry
stock system. As can be seen from Table 3, considerably improved
retention was obtained with the processes according to the present
invention.
TABLE 3 ______________________________________ Total polymer
addition, 1.2 kg/ton P3 + P2 P2 M2 M3 S1
______________________________________ Turbidity [NTU] 96 101 62 71
83 ______________________________________
EXAMPLE 4
First pass retention was evaluated as in Example 3, except that
other types of additives were used. The furnish was based on 80% of
a 80:20 mixture of peroxide bleached thermomechanical
pulp:stoneground wood pulp and 20% of the pulp according to Example
1. To the stock obtained were added 30% of china clay, based on dry
substance, 4 g/l of sodium acetate trihydrate and 10 mg/l of
extractives. Stock volume was 800 ml, consistency 0.15% and pH
5.5.
Polymer mixtures designated M4 and M5 were prepared by dissolving
HMW cationic polyacrylamide P1 according to Example 1 in aqueous
solutions of LMW polymers. The LMW polymer used in M4 was a
cationic polyacrylamide having a molecular weight of about 100,000
and a cationic charge density of 2.9 meq/g, which is designated P4
. M4 had a weight ratio P4 to P1 of 1:1. The LMW polymer used in M5
was a cationic starch having a molecular weight of about 400,000
and a cationic charge density of 2.5 meq/g, which is designated P5.
M5 had a weight ratio P5 to P1 of 1:1.
The polymer mixtures were compared to prior art processes in which
the polymers P1, P4 and P5 were separately added and where the LMW
polymers were added to the stock followed by stirring for 30
seconds before adding P1. The weight ratios of P4:P1and P5:P1were
both 1:1. These comparison tests are designated P4+P1 and P5+P1
.
The anionic inorganic particulate materials used were Sol 1
according to Example 1 and a silica sol of the type disclosed in
U.S. Pat. No. 4,388,150 which contained silica particles with a
specific surface area of 500 m.sup.2 /g, which is designated Sol 2.
The amount of Sol 1 and Sol 2 added was 3.0 and 6.0 kg/ton,
respectively, calculated as dry particles on dry stock system.
Table 4 shows the retention effect, measured as turbidity, when
using varying amounts of polymer, calculated as dry polymer on dry
stock system, in combination with the sols.
TABLE 4 ______________________________________ Polymer Sol
Turbidity [NTU] at polymer dosage [kg/ton] used used 1.0 2.0 3.0
4.0 6.0 8.0 10.0 ______________________________________ P4 + P1 Sol
1 100 72 50 44 -- 16 -- M4 Sol 1 80 59 45 40 -- 8 -- P4 + P1 Sol 2
-- -- -- -- 37 30 32 M4 Sol 2 -- -- -- -- 27 17 13 P5 + P1 Sol 1 --
62 -- 42 -- 13 13 M5 Sol 1 -- 61 -- 38 -- 9 4
______________________________________
EXAMPLE 5
The procedure of Example 4 was followed except that different
polymers were used. Cationic potato starch designated P6 was used
as the HMW polymer and the polyamine P3 according to Example 3 was
used as the LMW polymer. A polymer mixture designated M6 was
obtained by mixing the polymers in the form of aqueous solutions in
a weight ratio P6 to P3 of 5:1.
Table 4 shows the retention effect obtained with varying amounts of
P3+P6 and M6, calculated as dry polymer on dry stock system, when
the polymers were used in combination with Sol 1 added in an amount
of 3.0 kg/ton.
TABLE 5 ______________________________________ Polymer Turbidity
[NTU] at polymer dosage of used 18 kg/ton 24 kg/ton
______________________________________ P3 + P6 28 27 M6 20 18
______________________________________
EXAMPLE 6
Further cationic polymers and anionic inorganic particles were
evaluated for retention performance by means of a Britt Dynamic
Drainage Jar at a stirring speed of 1000 rpm, which is conventional
in the art. The stock and polymers used in Example 4 were similarly
used in this test series. The anionic inorganic particles used were
a suspension of the type disclosed in WO 94/05595 containing silica
based particles according to Example 1 and natural sodium bentonite
in a weight ratio of 2:1, designated Susp 1, and a suspension of
natural sodium bentonite, designated Susp 2. The amount of Susp 1
and Susp 2 added was 4.0 and 6.0 kg/ton, respectively, calculated
as dry on dry stock system.
Table 6 set forth the first pass retention of fines and filler at
varying polymer dosages, calculated as dry polymers on dry stock
system.
TABLE 6 ______________________________________ Retention [%] at
Polymer Suspension polymer dosage [kg/ton] used used 1 2 4 5
______________________________________ P4 + P1 Susp 1 26.1 32.2
56.7 70.5 M4 Susp 1 29.4 43.0 61.9 75.1 P4 + P1 Susp 2 -- 43.5 43.5
-- M4 Susp 2 -- 46.5 61.6 --
______________________________________
* * * * *